The present invention relates to an inductor device, in particular, relates to such a device which has a laminated toroidal magnetic core made of amorphous alloy and a winding wound on that magnetic core. The present invention is applicable, for instance, to a choke coil and a transformer.
A magnetic core for a choke coil or a transformer is conventionally made of ferrite material. And, lately, amorphous material is used for a core of a choke coil and/or a transformer instead of a ferrite material. Amorpuous material has the nature that the excellent rectangular B-H characteristics are obtained, the coercive force is extremely small, the loss in a core is small and so a small size of a transformer is obtained with low temperature-rise. Therefore, when an amorphous core is used as a core of a power transformer of an electric appliance, the power efficiency of the transformer is improved, and the wide range of voltage control and the stable temperature characteristics are obtained.
The amorphous material is usually shaped in a long sheet, or a ribbon, which is laminated or wound to a toroidal core.
However, a prior toroidal core has the disadvantages that the winding operation of a winding is difficult because of the toroidal shape of the core, it can not be used as an inductor which passes not only alternate current but also DC current with an air gap in a magnetic path.
The structure of FIG. 1 has been proposed for overcoming said disadvantages. In FIG. 1, the laminated toroidal core 1 is divided to two core halves 101 and 102, and an air gap G is provided between the two core halves. The structure of FIG. 1 has the advantages that the winding operation of a winding 2 is easy since the winding 2 may be wound on a bobbin 3 to which the core halves 101 and 102 are inserted, and that the magnetic characteristic are adjustable because of the presence of an air gap G. The inductor of FIG. 1 is manufactured as shown in FIGS. 2A and 2B, in which a loop magnetic core 1 is first produced as shown in FIG. 2A by winding a sheet of amorphous material, then, the loop core is cut to two core halves 101 and 102 as shown in FIG. 2B, then, those core halves are inserted into a bobbin 3 which has a winding 2.
However, the structure of FIGS. 2A and 2B has the disadvantages that the cut face 101a, 102a is not sufficiently smooth because of the cutting operation. Some sheets are even removed from the laminated body by the cutting operation. Because of the rough cut face, the length of an air gap G cannot be accurate. Further, because of the spring action of a core itself, the shape of the toroidal core is deformed. The deformation of the core shape changes the length of the air gap G, and then, even deteriorates the magnetic characteristics of the inductor itself. The air gap G has usually the length of 10-500 microns which must be very accurate, and that accuracy cannot be obtained by a prior producing method of FIGS. 1, 2A and 2B.